If you do a perlbrew switch in one window, the next run of
Flymake in a Perl buffer will automatically update your $PATH
in Emacs with the changes Perlbrew made.

Emacs-flymake-perlcritic
overrides the code that was changed, but has also been updated to take advantage of
the Perlbrew $PATH sync if it's available. This means that if you're using both
you'll need to update both to see the changes.